Method and device for casting a ring-shaped plastic frame in a recess of a rotor disk of a double-sided machining machine

ABSTRACT

A method for casting a ring-shaped plastic frame comprises providing two mold parts, wherein at least one of the two molds parts includes at least one ring-shaped seat. Positioning a rotor disk between the two mold parts where the rotor disk comprises at least one annular recess. Engaging a mold core with at least a portion of each of the two mold parts. The mold core comprises at least one casting channel configured to attach at one end to a supply of plastified plastic. Inserting at least one mold insert into the at least one ring-shaped seat. A mold volume is defined by the at least one mold insert, the mold core and an edge of the at least one annular recess, wherein the mold volume is configured to fluidly connect with the at least one casting channel to receive plastified plastic to form a plastic frame.

CROSS REFERENCE TO RELATED APPLICATION

This application is a divisional application of U.S. Non-Provisionalapplication Ser. No. 15/223,702, filed Jul. 29, 2016 and entitled METHODAND DEVICE FOR CASTING A RING-SHAPED PLASTIC FRAME IN A RECESS OF AROTOR DISK OF A DOUBLE-SIDED MACHINING MACHINE which claims the benefitand priority of German Patent Application No. 10 2015 112 527.7, filedJul. 30, 2015, under relevant sections of 35 USC § 119, the entirecontents of which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

The invention relates to a device for casting a ring-shaped plasticframe in a recess or annular recess of a rotor disk of a double-sidedmachining machine, The recess serves to hold a workpiece in thedouble-sided machining machine during the double-sided machiningprocess. The device comprises two mold parts that accommodate the rotordisk between themselves, and a mold core that partially fills in therecess when the rotor disk is accommodated between the mold parts,wherein the mold core has at least one casting channel. One end of themold terminates in a mold volume provided for the plastic frame and theother end is connectable to a supply for plastified plastic. Theinvention also relates to a corresponding method. Finally, the inventionrelates to a rotor disk of a double-sided machining machine.

A double-sided rotor disk is known for example from DE 102 28 441 B4.The rotor disks generally have a plurality of recesses in whichworkpieces, in particular semiconductor wafers, are held floating duringmachining in the double-sided machining machine. Suitable kinematicscause the rotor disks to move between the working gap formed between themachining disks such that they describe cycloid paths through theworking gap in the semiconductor wafers held in the recesses of therotor disks. The rotor disks normally consist of wear-resistantmaterials such as metal. To keep the semiconductor wafers from beingdamaged, the edge of the recesses of the rotor disks is normallyprovided with a plastic frame which is cast in the contour edge of therotor disks in a casting procedure, such as a plastic injection moldingprocedure.

Extremely high demands are placed upon the dimensions of thesemiconductor disks, such as silicon wafers, to be generated. Thesedimensions are significantly influenced by the consumable materials usedduring machining. For example in the case of double-sided polishing, beit abrasive polishing or haze-free polishing, the tolerances for globalparallelism (GBIR), local flatness (SFQR), edge flatness (ESQFR) and thecurvature of the top and bottom side of the wafer at the semiconductoredge (ZDD) are becoming increasingly smaller. The rotor disks and inparticular the plastic frames play a decisive role since they influencethe interaction between a polishing cloth applied to the working disksand the wafer edge. The plastic frame interacts with the polishing clothdepending on its thickness with reference to the semiconductorthickness, which in turn influences the polishing pressure at the edgeof the wafer. For example, strong polishing cloth compression due to theplastic frame yields weak pressure by the polishing cloth on the waferedge and vice versa.

For specific workpiece dimensions, in particular at the workpiece edge,the precise arrangement and dimensions of the plastic frame are highlyimportant. With the known method, critical parameters such as thealignment of the plastic frame relative to the rotor disk main body, andhence a specific step height between the rotor disk and plastic frame,cannot be controlled in the desired manner. This can produce axiallyasymmetrical plastic frames with reference to the rotor disk. This inturn causes an uneven curvature of the semiconductor wafer edges aftermachining and hence an impairment of the local flatness. A spread of theframe dimensions, in particular the frame thickness occurring in knownmethods for producing plastic frames yield undesirable deviations in thedimensions of the semiconductor wafers machined in the machine. Duringthe known casting methods, deviations in dimensions arise, for exampledue to the shrinkage of the material used and the parameters used in thecasting method.

BRIEF SUMMARY OF THE INVENTION

On the basis of the explained prior art, the object of the invention isto provide a device, method and a rotor disk of the above-cited type,wherein the dimensions and arrangement of the plastic frame in therecesses of the rotor disks, and hence the machining results of theworkpieces machined with the rotor disks, can be precisely controlled ina flexible manner.

For a device for the aforementioned type, the invention achieves theobject in that least one of the mold parts has at least one annularpocket or ring-shaped seat in which at least one ring-shaped mold insertis releasably inserted such that the at least one ring-shaped moldinsert, together with the mold core and the edge of the recess, delimitsthe mold volume provided for the plastic frame.

The invention furthermore achieves the object by a method for casting aring-shaped plastic frame in a recess of a rotor disk of a double-sidedmachining machine, wherein the recess serves to hold a workpiece duringdouble-sided machining in the double-sided machining machine, asdescribed in the following steps.

A rotor disk is accommodated between two mold parts, and the recess ispartially filled with a mold core while the rotor disk is accommodatedbetween the mold parts, wherein the mold core has a least one castingchannel, one end of which terminates in a mold volume provided for theplastic frame, and the other end of which is connectable to a supply forplastified plastic, at least one ring-shaped mold insert of at least oneof the mold parts is releasably inserted into at least one ring-shapedseat of at least one of the mold parts such that the at least onering-shaped mold insert, together with the mold core and the edge of therecess, delimits the mold volume provided for the plastic frame. Theplastified plastic from the supply is then cast in the mold volumeprovided for the plastic frame through the at least one casting channelof the mold core. Once sufficient stability of the shape of the castplastic is achieved, the rotor disk is removed along with the plasticframe cast in the recess.

The rotor disks can, for example, consist of a metal material. Howeverin another embodiment, a plastic material is also conceivable. The rotordisk possesses at least one, but generally a plurality, of recesses, inwhich workpieces such as semiconductor wafers are held floating duringdouble-sided machining, for example double-sided polishing. As mentionedabove, the rotor disks move while rotating during double-sided machiningthrough the working gap between the working disks of the double-sidedmachining machine such that the workpieces to be machined describecycloid paths through the working gap. The work piece such assemiconductor wafers and the recesses in the rotor disk provided for thesemiconductor wafers can for example be circular. The plastic frame castin the recess can be correspondingly ring-shaped and is injected ontothe inner surface of the rotor disk delimiting the recess in a moldingmethod such as a plastic injection molding method. However, othermolding methods are also conceivable with the invention such ascentrifugal casting methods.

According to the invention, the rotor disk is in particular clampedbetween the mold parts. The mold parts can be mold plates. Inparticular, the mold parts can be mold halves. More than two mold partscan also be provided. The inner surface of the rotor disk delimiting therecess, the mold inserts, or respectively the ring-shaped mold insertsand the mold core, delimit the mold cavity forming the plastic frame.Plastified plastic is cast, such as injected, into this mold cavity. Forthis purpose, the mold core has at least one casting channel, one end ofwhich is connected to a supply for a molten plastic such as from anextruder, and the other end of which is connected to the mold cavity.The mold core can in particular possess a plurality of such castingchannels. Of course, a plurality of such mold cores can also beprovided.

At least one of the mold parts has at least one ring-shaped seat inwhich the at least one ring-shaped mold insert is releasably inserted.Together with the mold core and the edge of the recess, the at least onering-shaped mold insert delimits the mold volume provided for theplastic frame. The at least one mold insert can for example be screwedto the least one mold part. However, other types of fastening are alsopossible. The mold inserts as well as the mold parts can also consistfor example of a metal material. They can possess a surface roughnessadapted to the plastic material to be cast to prevent adhesion of themolten material.

The mold inserts according to the invention in the mold allow theposition and dimensions to be precisely controlled in a flexible manner,in particular the thickness, of the cast plastic frame in comparison tothe main body of the rotor disk. By means of the mold inserts accordingto the invention, the position of the plastic frame can be adjustedwithin a range of, for example, +/−20 μm relative to the top, orrespectively bottom of the rotor disks. This results in possibledifferences in thickness between the plastic frame and rotor disk mainbody of for example −40 μm to +40 μm. Fluctuations in the thicknessvalues of the cast plastic frame can be minimized by the ring-shapedmold inserts according to the invention. A specific plastic framethickness can be reliably adjusted in a flexible manner. The same holdstrue for the step dimensions between the plastic frame and the main bodyof the rotor disk. Given the specific adjustment of the plastic framedimensions and arrangement according to the invention, a low injectionpressure in the plastic injection molding method and a homogeneouscrystalline structure of the plastic, the plastic frame dimensions canbe optimally harmonized with requirements of the double-sided machining,in particular the double-sided polishing process. By using rotor diskswith plastic frames produced according to the invention, workpieces, inparticular semiconductor wafers, can be produced with optimum dimensionswhich in particular also holds true for the edge of the workpieces. Forexample, the spread of the thickness of the plastic frame can, forexample, be limited to ±5 μm, preferably ±2 μm, more preferably ±1 μmwith the method according to the invention, or respectively the deviceaccording to the invention.

According to one embodiment, the mold parts can each have at least onering-shaped seat in which at least one ring-shaped mold insert isreleasably inserted such that the ring-shaped mold inserts together withthe mold core and the edge of the recess delimit the mold volumeprovided for the plastic frame. In this embodiment, the plastic frame isformed on both sides by mold inserts releasably attached within the moldparts to increase flexibility and precision.

According to another embodiment, the device can comprise a plurality ofdifferently dimensioned ring-shaped mold inserts that optionally arereleasably insertable into the at least one ring-shaped seat such thatdifferently dimensioned mold volumes for plastic frames can be generatedby inserting differently dimensioned ring-shaped mold inserts. Thisfurther improves the flexibility. With only one mold, different plasticframe dimensions can be realized by exchanging the ring-shaped moldinserts.

According to one embodiment, the mold volume that is delimited by the atleast one ring-shaped mold insert together with the mold core and theedge of the recess and is provided for the plastic frame can possess alonger extension than the rotor disk in the axial direction of therecess. By means of this embodiment, a plastic frame can be formed withthe same thickness as the rotor disk despite the unavoidable shrinkageduring the cooling and hardening of the plastic.

According to another embodiment, the mold volume provided for theplastic frame can have one or more cavities for feeders. Feeders orrespectively risers are then formed in the produced plastic frame thatcounteract the formation of cavities during the hardening process.

According to another embodiment, a heating device can be provided bymeans of which the at least one casting channel is heated. The use ofsuch a heated channel produces an even temperature in the moltenplastic, and the flow paths can be kept short. In addition, theinjection pressure can thereby be reduced to ensure optimum molding ofthe precise mold dimensions and in particular a homogeneouscrystallization of the thermoplastic material. Homogeneouscrystallization yields greater dimensional stability of the producedplastic frame.

The optimum casting geometry with sufficient areas for venting the moldand a regular arrangement of feeders further simplifies the minimizationof the injection and holding pressure.

The method according to the invention can be performed by the deviceaccording to the invention. Accordingly, the device according to theinvention can be suitable to perform the method according to theinvention.

The invention furthermore relates to a rotor disk of a double-sidedmachining machine with at least one recess, and at least one ring-shapedplastic frame cast in the at least one recess using the method accordingto the invention. The rotor disk can in particular be a rotor disk for adouble-sided polishing machine.

For example, the thermoplastic materials cited in the following tableare materials that can be used according to the invention for theplastic frame, wherein the left column lists unfilled materials, and theright column lists material that are filled, or respectively providedwith a fiber component:

Thermoplastic materials Unfilled Filled PEEK PPS GF 40 PTFE PA 66 GF 50PFA PA 66 GF 25 PA 66 PBT GF 50 PET PBT GF 30 PBT PES GF 30 PES PES GF20 PA 6 PA6 GF 50 PEI PA6 GF 25 PPSU PEI GF 30 PSU PSU GF 30 PA 12 PSUGF 20 PVDF PA 12 GF 30 POM-H PVDF CF 10 PP-H PP GF 40 LF PPO PP GF 30 PCPP GF 20 PE-HD POM GF 25 PE-UHMW PC GF 30 PC + ABS PC GF 10 V0 ABS PPOGF20 PE-LD PC + ABS GF 20 PMMA SAN GF 35 SAN ABS GF17 PS

BRIEF DESCRIPTION OF THE DRAWINGS

In the following, the invention is explained in more detail withreference to the figures. Schematically,

FIG. 1 shows a sectional view of an embodiment of the casting device,

FIG. 2 shows a sectional enlargement of a region of an embodiment of thecasting device in a first operating state schematically portrayed at Ain FIG. 1,

FIG. 3 shows the casting device of FIG. 2 in second operating state,

FIG. 4 shows the casting device of FIG. 2 in a third operating state,

FIG. 5 shows the perspective view from FIG. 4 according to anotherexemplary embodiment,

FIG. 6 shows excerpts of sectional views of rotor disks with differentplastic frames produced by the method according to the invention, and

FIG. 7 shows an example of a plastic frame produced using the methodaccording to the invention, or respectively the device according to theinvention.

DETAILED DESCRIPTION OF THE INVENTION

If not otherwise specified, the same reference numbers indicate the sameobjects in the figures. The device shown in FIG. 1 has a first mold part10, in particular a first mold half, and a second mold part 12, inparticular a second mold half A rotor disk 14 of a double-sidedmachining machine, in particular a double-sided polishing machine, isclamped between the mold parts 10, 12 and accordingly held. The rotordisk 14 possesses a plurality of for example circular recesses 16 ofwhich one can be seen in FIG. 1. During operation, e.g. circularsemiconductor wafers such as silicon wafers are held floating in therecesses 16 to be machined in a double-sided machining machine. Thedevice shown in FIG. 1 furthermore has a mold core 18 which is insertedin the recess 16 and fills it up to a mold cavity 20. In one embodiment,the mold cavity 20 is ring-shaped. Reference signs 22, 24 schematicallyindicate casting channels formed in the mold core 18 in FIG. 1. At itstop end in FIG. 1, the central casting channel 22 is connected to asupply (not shown) for molten plastic such as an extruder. The castingchannels 24 connected to the central casting channel 22 terminate in themold cavity 20. During operation, the molten plastic is conducted fromthe supply through the casting channels 22, 24 into the mold cavity 20as indicated by the arrows in FIG. 1.

In FIG. 2, it can be seen that in the device according to the invention,the mold parts 10, 12 each have a ring-shaped pocket, such as a circularring-shaped seat, wherein a ring-shaped component, such as a circularring-shaped mold insert 26, 28 is releasably inserted into thering-shaped seat. The mold inserts 26, 28 can for example be screwed tothe mold parts 10, 12. As can be seen in FIG. 2, the mold cavity 20,which is also ring-shaped, e.g. circular ring shaped, is delimited bythe mold core 18, the inner edge of the rotor disk 14 forming the recess16 and the insides of the annular ring-shaped mold inserts 26, 28. Thismold cavity 20 forms the mold volume provided for the plastic frame tobe cast in the rotor disk 14.

FIG. 3 depicts the operating state shortly after casting still meltableplastic 30 through the mold channels 22, 24 in the mold cavity 20. Itcan clearly be seen in FIGS. 2 and 3 that the mold cavity 20 providedfor the plastic frame possesses a longer extension than the rotor disk14 in the axial direction of the recess 16, i.e., from bottom to top inFIGS. 2 and 3. Correspondingly, the still flowable plastic materialprojects slightly above the top and bottom of the rotor disk 14 in FIG.3. By means of this embodiment, the shrinkage is compensated that occurswhile the plastic material cools and dries. FIG. 4 shows the hardenedstate of the plastic material 30 forming the plastic frame. As can beeasily discerned in FIG. 4, the plastic material 30 is flush with thetop side and bottom side of the rotor disk 14 in this hardened state.Merely for the sake of completeness, it is noted that the gap which canfor example be discerned in FIG. 3 between the top side, or respectivelythe bottom side of the rotor disk 14 and associated surfaces of the moldinserts 26, 28 is small enough so that the plastified plastic 30 cannotpenetrate into this gap due to its viscosity.

The embodiment in FIG. 5 differs from the embodiment shown in FIGS. 2 to4 such that the ring-shaped mold insert 26′ inserted into the top moldpart 10 is thicker than the ring-shaped insert 26′ shown in FIGS. 2 to4. FIG. 5 shows the cooled and hardened state of the plastic material30. In FIG. 5, it can be seen that, due to the greater thickness of themold insert 26′, the hardened plastic 30 does not extend completely upto the top side of the rotor disk 14.

With the device according to the invention, or respectively the methodaccording to the invention, precise desired dimensions of the plasticframe formed by the plastic material 30 can be flexibly produced byappropriately selecting the respective cast inserts. Different framegeometries that are possible by means of the invention are shown as anexample in FIG. 6.

FIG. 7 shows a plastic frame 32 without the rotor disk for reasons ofillustration that is produced by means of the method according to theinvention, or respectively the device according to the invention. It canbe seen that the plastic frame 32 has a dovetailed shape 34 at its outerperimeter which corresponds to a an equivalent dovetailed shape on theinner surface of the recess 16 in the rotor disk 14. At reference signs36, 38, feeders, or respectively risers can also be seen distributed atregular intervals across the inside of the plastic frame 32 which weregenerated during the plastic injection molding process. These feedersare removed during the finishing of the plastic frame 32. These are inparticular to prevent the formation of cavities during the plasticinjection molding process and enable lower injection and holdingpressures. This in turn produces more homogeneous crystallization of theplastic material 30 and hence improved shape retention of the plasticframe 32.

By means of the invention, precisely centered plastic frames can beproduced in the axial direction of the recesses of the rotor disks. Adeviation in thickness in this axial direction can be limited forexample to ±5 μm, preferably ±2 μm, and more preferably ±1 μm. Thisholds true in particular for each location of the plastic frame that isat least 0.5 mm and at most 1 mm distant from an inner edge of theplastic frame. The deviation in thickness of the plastic frame can forexample lie within a bandwidth of 10 μm, preferably 4 μm, morepreferably 2 μm around a target value, for example for at least 90% ofits lateral extension within an area of 0.5 mm to 1 mm from an inneredge.

All of the indicated values are with reference to room temperature anddry rotor disks with plastic frames that have only experiencedabsorption of water only from normal ambient air.

The invention claimed is:
 1. A method for casting a ring-shaped plasticframe into at least one circular recess in a rotor disk adapted toaccommodate wafers for machining in a double-sided machining machine,the method comprising: providing a first mold part comprising at leastone annular pocket; providing a second mold part comprising at least oneannular pocket; positioning a rotor disk at least partially between thefirst mold part and the second mold part; positioning a first releasablemold insert within the at least one annular pocket of the first moldpart; positioning a second releasable mold insert within the at leastone annular pocket of the second mold part; and engaging a mold corewith the first mold pant and the second mold part, Wherein the mold corecomprises at least one casting channel configured to connect at one endto a supply of casting material, wherein a mold volume is defined by thefirst releasable mold insert, the second releasable mold insert, therotor disk, and the mold core, and wherein the mold volume is fluidlyconnected to the at least one casting channel.
 2. The method accordingto claim 1, herein the at least one annular pocket of at least one ofthe first mold part and the second mold part is configured toaccommodate a plurality of differently dimensioned releasable moldinserts.
 3. The method according to claim 1, wherein the mold volumeextends beyond the circular recess of the rotor disk in an axialdirection.
 4. The method according to claim 1, wherein the mold volumeincludes one or more additional cavities configured for feeders.
 5. Themethod according to claim 1, wherein the at least one casting channel isheated.
 6. A method for casting a ring-shaped plastic frame, the methodcomprising: providing two mold parts, wherein at least one of the twomolds parts includes at least one ring-shaped seat; positioning a rotordisk between the two mold pans, the rotor disk comprising at least oneannular recess; engaging a mold core with at least a portion of each ofthe two mold parts, the mold core comprising at least one castingchannel configured to attach at one end to a supply of plastified pplastic; and inserting at least one mold insert into the at least onering-shaped seat, wherein a mold volume is defined by the at least onemold insert, the mold core and an edge of the at least one annularrecess, wherein the mold volume is configured to fluidly connect with anopposite end of the at least one casting channel, and wherein the moldvolume is configured to receive plastified plastic from the at least onecasting channel to form a plastic frame.
 7. The method according toclaim 6, wherein at least one mold insert is releasably inserted in atleast one ring-shaped seat of each of the mold parts such that the atleast one mold insert together with the mold core and the edge of the atleast one annular recess delimit the mold volume provided for theplastic frame.
 8. The method according to claim 6, wherein the at leastone ring-shaped seat is configured to accommodate differentlydimensioned mold inserts for casting differently dimensioned plasticframes.
 9. The method according to claim 6, wherein the mold volume isat least partially defined by a portion of the rotor disk, and whereinthe mold volume extends beyond the at least one annular recess of therotor disk in an axial direction.
 10. The method according to claim 6,wherein one or more feeders is formed on the plastic frame.
 11. Themethod according to claim 6, wherein the at least one casting channel isheated.
 12. The method according to claim 6, wherein the mold volumeincludes one or more additional cavities configured for feeders.